The Applicant's International PCT Patent Application Nos. PCT/AU00/00654 and PCT/AU01/01187 disclose heart assist devices, systems and methods. More particularly, these specifications disclose vessel deformers in the form of inflatable balloon or chambers which form part of implantable counter-pulsation heart assist devices. The balloon or chambers are cyclically inflated and deflated and used to compress the patient's ascending aorta during diastole and release the compression during systole.
The balloon or chamber are generally secured to the aorta by a substantially non-elastic wrap or sheath, which is secured around a section of the aorta with the balloon or chamber therebetween. For the heart assist device to function efficiently, it is necessary that the wrap be a snug fit around the aorta when the balloon or chamber is deflated.
Hitherto, wraps have been manufactured from a length of substantially inflexible woven polyester material. The disadvantage of known wraps will be described with reference to FIG. 3 which shows a section of aorta 10 encased by a known wrap 12. If the wrap 12 is over-tightened (as shown), its sides cause a sharp depression or kink in the aorta 10, in the regions indicated by the reference numeral 14. This can also occur due to the aorta 10 enlarging slightly as the patient recovers or with age. This depression/kinking places a higher strain on the wall of the aorta 10 and can damage same. Also, the kink in the internal wall of the aorta 10 induces turbulence in the blood flow, which increases the likelihood of plaque formation.
Wrapping a curved vessel with a flat straight piece of fabric also leads to bunching or folding of the fabric. This is undesirable as it encourages secondary growth or potential infection in the bunched/folded region and results in uneven load distribution.
It is also known to place static wraps around blood vessels, for instance to reinforce vessels suffering from aneurysmal disease.
Any aortic compliance may be lost by placement of non-elastic or non shape-changing wrap, which may reduce the natural advantage of aortic compliance on cardiac function.
It is an object of the present invention to provide a wrap that substantially overcome or at least ameliorate one or more of the above disadvantages.